CVE-2020-6830 in Firefox
Summary
by MITRE
For native-to-JS bridging, the app requires a unique token to be passed that ensures non-app code can't call the bridging functions. That token was being used for JS-to-native also, but it isn't needed in this case, and its usage was also leaking this token. This vulnerability affects Firefox for iOS < 25.
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Analysis
by VulDB Data Team • 05/27/2020
The vulnerability described in CVE-2020-6830 represents a critical security flaw in the native-to-JavaScript bridging mechanism of Firefox for iOS versions prior to 25. This issue stems from improper token validation across different communication pathways within the application's architecture, creating a significant attack surface that could be exploited by malicious actors. The bridge mechanism serves as a crucial interface between the native iOS components and JavaScript execution environment, making its security paramount to the overall application integrity.
The technical flaw manifests in the improper reuse of a security token designed specifically for native-to-JS communication. This token serves as a verification mechanism to ensure that only legitimate application code can invoke the bridging functions. However, the implementation error extends this token's validation to JS-to-native calls where such protection is unnecessary and actually harmful. The vulnerability creates a scenario where the security token becomes exposed during JavaScript execution, allowing unauthorized code to potentially bypass security controls and execute privileged operations.
This flaw directly impacts the application's security model by creating a token leakage vulnerability that violates fundamental principles of access control and privilege separation. The improper token usage creates a path for privilege escalation attacks, where malicious JavaScript code could potentially leverage the leaked token to make unauthorized native calls. The vulnerability affects Firefox for iOS versions before 25, indicating that this was a specific implementation issue within the mobile browser's architecture that was not adequately addressed in the affected releases.
From an operational perspective, this vulnerability could enable attackers to execute arbitrary native code on iOS devices running vulnerable versions of Firefox. The impact extends beyond simple information disclosure, as it could allow for full system compromise through unauthorized access to native APIs and system resources. This type of vulnerability aligns with CWE-284 Access Control Issues, specifically targeting improper access control mechanisms in cross-platform communication bridges. The vulnerability also relates to ATT&CK technique T1059 Command and Scripting Interpreter, where attackers could potentially use the compromised bridge to execute malicious commands through JavaScript manipulation.
The recommended mitigation strategy involves implementing proper token validation mechanisms that distinguish between native-to-JS and JS-to-native communication pathways. This requires removing the unnecessary token validation from JS-to-native calls while maintaining robust security controls for native-to-JS interactions. Organizations should immediately update to Firefox for iOS version 25 or later, which contains the necessary fixes to address this vulnerability. Additionally, security teams should conduct thorough code reviews of similar bridging mechanisms in other applications to identify potential instances of token leakage or improper access control implementation. The fix typically involves implementing separate security tokens or validation mechanisms for each communication direction, ensuring that the security model maintains proper isolation between JavaScript and native execution environments.